Disruption of the gut epithelial barrier occurs commonly in various critical surgical conditions such as trauma, burns, hemorrhage, sepsis, and massive surgical operations, leading to the translocation of luminal toxic substances and bacteria to the blood stream. Since the exact mechanism underlying the acute epithelial barrier dysfunction remains obscure, effective therapies to preserve the integrity of the barrier are limited, contributing to death in critically surgical patients with leaky gut. During previous funding period, we have established that decreased expression of occludin and ZO-1 in the tight junction (TJ) and E-cadherin in the adherens junction (AJ) plays an important role in increased intestinal epithelial paracellular permeability, and have identified a novel mechanism through which cellular polyamines regulate transcription of the genes encoding these intercellular junctional proteins. However, the exact mechanism underlying posttranscriptional regulation of TJs and AJs in critical surgical conditions remains largely unknown and is the focus of this competitively renewal application. Our preliminary results indicate a) RNA-binding protein (RBP) HuR binds to the occludin mRNA, while HuR silencing represses occludin translation; b) HuR- binding affinity decreases significantly in critical surgical stress; and c) decreasing cellular polyamines not only inhibits HuR-binding to occludin mRNA but also induces cytoplasmic levels of the translational repressor TIAR. Based on these observations, we HYPOTHESIZE that 1) RBPs HuR and TIAR play an important role in the regulation of the intestinal epithelial barrier function by modulating the stability and translation of TJ mRNAs in critical surgical conditions and 2) cellular polyamines regulate occludin translation by altering HuR and TIAR activities. Three specific aims are proposed to test the hypotheses: 1) to determine the roles of HuR and TIAR in TJ expression and barrier dysfunction during critical surgical stress by using tissue-specific genetic modification strategy; 2) to define the exact roles of HuR and TIAR in the posttranscriptional regulation of TJ protein expression; and 3) to investigate the mechanism by which polyamines regulate occludin translation during surgical stress. Completion of these specific aims will provide novel information regarding the posttranscriptional regulation of TJs and also yield a novel model in which occludin translation is regulated by polyamines during surgical stress. It is hoped that our findings will identify factors and mechanisms that can be used to protect the epithelial barrier in patients with critical surgical illnesses. PUBLIC HEALTH RELEVANCE: Increased gut permeability occurs commonly during various critical surgical disorders such as trauma, thermal injury, shock, sepsis, and massive surgical operations, leading to the translocation of luminal toxic substances and bacteria to the blood stream. Since the exact mechanism underlying this acute epithelial barrier dysfunction remains obscure, effective therapies to preserve the integrity of the barrier are limited, contributing to death in critically surgical patients with leaky gut. Completion of this project will identify the pathogenesis of the barrier dysfunction in critical surgical conditions and provide a fundamental base for development of new therapies to protect the gut barrier in patients with critical surgical illnesses.